This invention relates to the manufacture of vehicle tires and more particularly relates to the portion of the manufacturing process by which the quality of the tire sidewalls is maintained.
The tire industry has long sought an automated method of improving the quality of single-ply tires. Such tires weigh less and cost less than multiple ply tires and therefore are particularly attractive for use on light-weight economy vehicles.
While single-ply tires have become attractive for use on economy cars, certain problems inherent with those tires have become apparent. A particular problem evolves from irregularities in the ply splice at the sidewall of the tire. If this splice is other than a flush butt fit, the sidewall at the splice may exhibit undesired characteristics. For example, if the splice is lapped, the sidewall becomes exceptionally strong at that point, being effectively a double-ply at the splice. When inflated, the sidewall at the splice may not expand to the same degree as the sidewall as a whole, thus generating a deformation commonly termed a "valley." While this valley is an indication of exceptional strength at that point of the sidewall, if the valley is excessive, it becomes unsightly and therefore unmarketable. In the case of an open splice, the sidewall is weakened such that, when inflated, the weakened area at the splice will excessively expand to define a deformation commonly termed a "bulge." Such a bulge is not only an indication of a weakened area in the sidewall, but becomes unsightly if excessive.
Bulges and valleys are peculiar to single or mono-ply tires, since tires of multiple plies are typically of sufficient strength to be unaffected by an open or lapped splice in any of the plies. In a single ply tire, an open splice results in reduced ply strength at the affected area of the sidewall, while a lapped splice results in an effective doubling of the strength at that area.
Since the undesirability of a bulge or valley is partially aesthetic, different users of the tires will have different specifications for determining the maximum dimensions of valleys or bulges (or both) which are acceptable. Ideally, the tire quality control portion of the manufacturing process should be conveniently adaptable to different specifications.
There have been several teachings in the art of apparatus for sensing and testing the dimensional characteristics of a tire. Applicant is aware of U.S. Pat. Nos. 3,895,518; 3,303,571; and 2,25,803, all of which teach a technique for monitoring the sidewall of a tire. However, each of these patents is of a rudimentary mechanical nature, capable of sensing only that the sidewall of a mounted tire has exceeded the limit unassociated with the tire itself.
U.S. Application Ser. No. 270,087, "Method and Apparatus For Tire Sidewall Bulge And Valley Detection," filed June 3, 1981 in the name of Jean Engel and assigned to the assignee of the present application, now U.S. Pat. No. 4,402,218 issued Sept. 6, 1983 discloses an improvement in the art of detecting sidewall deformations by measuring the slope of the sidewall bulges or valleys with analog circuitry. However, this technique is somewhat less accurate than desired for certain applications, especially if the quality control specification for the tire requires that a bulge be distinguished from a valley.
Accordingly, it is a primary object of the present invention to improve the manufacture of tires by furnishing an automated digital technique for accurately and rapidly determining the extent of sidewall deformations in a tire.
Another object is to provide a technique of the foregoing type capable of distinguishing sidewall bulges from valleys.
Still another object is to provide a technique of the foregoing type in which test criteria can be rapidly and accurately changed to accommodate different tire specifications.
Yet another object is to provide a technique of the foregoing type in which different limits can be used to detect excessive bulges and valleys.
Another object is to provide a technique of the foregoing type particularly adapted to distinguish a sidewall bulge and a sidewall valley adjacent to each other.
Yet a further object is to provide a technique of the foregoing type in which a single limit can be used to detect excessive bulges and valleys that are adjacent or nonadjacent.
In order to achieve these objectives, the applicant has totally departed from the analog differentiating and slope comparing circuitry of Engel. The applicant has discovered that digital circuitry, including a memory and processor, provides more accurate results. According to one aspect of this invention, the processor divides data from the tire sidewall into a plurality of groups which are individually analyzed. The results and then combined and compared with a predetermined limit which can be readily altered. According to another aspect of the invention, in each group, the highest data value is subtracted from the lowest data value to obtain a peak-to-peak value. The largest peak-to-peak value is stored in order to evaluate the sidewall deformations of the tire. By these techniques, the condition of a tire can be indicated with a degree of accuracy and reliability previously unobtainable.